Different metals produce different colours when heated by a hot flame. Flame tests are carried out on samples of ionic substances. The most intense colours are obtained from solids. However, flame tests can also work when the solids have been dissolved in water. Flame tests have helped scientists discover new compounds such as caesium and rubidium when they produce and unfamiliar colour. Certain colours represent certain metals. For example: Sodium (Na+) = yellow. Potassium (K+) = lilac. Calcium (Ca2+) = red. Copper(II) (Cu2+) = green/blue.
Precipitation tests are used to identify certain anions. To identify ions such as aqueous chloride ions, a few drops of dilute nitric acid are added to the sample solution, which is then shaken. A few drops of silver nitrate solution are then added. A white precipitate of silver chloride forms if the sample contains chloride ions.